Semiconductor device

ABSTRACT

A semiconductor device includes rectifying elements which are connected in series and has a rectifying function from a first input terminal portion to an output terminal portion; a first wiring and a second wiring, which are connected to a second input terminal portion; and a boosting circuit including a plurality of capacitor elements each having a first electrode, an insulating film, and a second electrode and storing a boosted potential. The plurality of capacitor elements includes a capacitor element in which the first electrode and the second electrode are formed using conductive films, and a capacitor element in which at least the second electrode is formed using a semiconductor film. In the plurality of capacitor elements, at least a capacitor element in a first stage is a capacitor element in which the first electrode and the second electrode are formed using conductive films.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/957,560, filed Dec. 17, 2007, now allowed, which claims the benefitof a foreign priority application filed in Japan as Serial No.2006-354427 on Dec. 28, 2006, both of which are incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having aboosting circuit, in particular, a semiconductor device having aboosting circuit which supplies a potential higher than power sourcevoltage.

2. Description of the Related Art

A boosting circuit is used for a variety of purposes, for example, for aCCD driver circuit, an organic EL driver circuit, a low-temperaturepolysilicon liquid crystal driver circuit, a white light emitting diodedriver circuit, an RF circuit, and a multiple power source system. Forexample, reduction in voltage in a semiconductor device such as a flashmemory is accompanied by boosting power source voltage for obtaininghigh voltage necessary for writing or erasing data. In recent years, aboosting circuit which has a small area and efficiently generates highvoltage has been expected in various fields, with the higher integrationof integrated circuits of semiconductor devices.

In order to reduce the area of a boosting circuit, use of a MOScapacitor using a semiconductor substrate having a conductivity type oran insulating film having high dielectric constant, as a capacitor (acapacitor element), is proposed (for example, Reference 1: JapanesePublished Patent Application No. 2003-297936). In Reference 1, asemiconductor substrate having a conductivity type is used for one ofelectrodes of a MOS capacitor, and a conductive film corresponding to agate electrode is used for the other of the electrodes, and aninsulating film corresponding to a gate insulating film of a transistoris provided between the two electrodes to increase capacitance per unitarea.

SUMMARY OF THE INVENTION

However, in a semiconductor device, in the case where an element such asa boosting circuit is formed using a thin film transistor (hereinafter,also referred to as “TFT”) and one of electrodes of a capacitor elementis formed using a semiconductor film having a conductivity type, animpurity element is necessary to be selectively introduced into asemiconductor film to be the one of the electrodes of the capacitorelement after forming the semiconductor film over a substrate. Thus,there is concern that the number of manufacturing steps is increased orthat a semiconductor film into which an impurity element is notintroduced is contaminated. Moreover, in the case where a semiconductorfilm into which an impurity element is not introduced is used for anelectrode of the capacitor element, there is a fear that the capacitorelement does not serve as a capacitor when voltage applied to one end ofthe capacitor element (voltage obtained by subtracting threshold voltageof a rectifying element from input voltage) is lower than thresholdvoltage of the capacitor element of a thin film transistor type.

In view of the foregoing problems, it is an object of the presentinvention to provide a semiconductor device of which a manufacturingprocess is simplified and which has a boosting circuit in which the areaof a capacitor element is reduced.

A semiconductor device of the present invention includes a plurality ofrectifying elements, which is connected in series and has a rectifyingfunction from a first input terminal portion to an output terminalportion; a first wiring and a second wiring, which are connected to asecond input terminal portion, into which a signal and a signal obtainedby inverting the signal are respectively input; and a boosting circuitincluding capacitor elements each having a first electrode, aninsulating film, and a second electrode. The first electrode isconnected to an output portion of a rectifying element of the pluralityof rectifying elements and an input portion of another rectifyingelement of the plurality of rectifying elements, which is adjacent tothe rectifying element; the second electrode is connected to the firstwiring or the second wiring; the plurality of capacitor elementsincludes a capacitor element in which the first electrode and the secondelectrode are formed using conductive films, and a capacitor element inwhich at least the second electrode is formed using a semiconductorfilm; and, in the plurality of capacitor elements, at least a capacitorelement in a first stage is a capacitor element in which the firstelectrode and the second electrode are formed using conductive films.

In the above-described structure, the semiconductor device of thepresent invention can have a structure in which the rectifying elementis a diode-connected thin film transistor; and a gate electrode of thethin film transistor, the first electrode of the capacitor element inthe first stage, and a first electrode of the capacitor element in whichthe second electrode is provided using a semiconductor film, are formedusing a same material.

A semiconductor device of the present invention includes a plurality ofrectifying elements, which is connected in series and includes at leasta first rectifying element, a second rectifying element, and a thirdrectifying element which have a rectifying function from a first inputterminal portion to an output terminal portion; a first wiring and asecond wiring, which are connected to a second input portion; and aboosting circuit including a plurality of capacitor elements having afirst capacitor element provided in a first stage and a second capacitorelement provided in a second stage. The plurality of capacitor elementsincludes a capacitor element in which the first electrode and the secondelectrode are formed using conductive films, and a capacitor element inwhich at least the second electrode is formed using a semiconductorfilm; the first electrode of the first capacitor element is connected toan output portion of the first rectifying element and an input portionof the second rectifying element; the second electrode of the firstcapacitor element is connected to the first wiring; the first electrodeof the second capacitor element is connected to an output portion of thesecond rectifying element and an input portion of the third rectifyingelement; the second electrode of the second capacitor element isconnected to the second wiring; and at least the first capacitor elementis a capacitor element in which the first electrode and the secondelectrode are formed using conductive films. Further, the secondcapacitor element may be a capacitor element in which the secondelectrode is formed using a semiconductor film.

According to the present invention, by providing a capacitor element ofa thin film transistor type for each capacitor element of a boostingcircuit, the area of the boosting circuit can be reduced. Further, byproviding one of electrodes of a capacitor element using a semiconductorfilm formed in the same step as a semiconductor film forming a channelformation region of a TFT, a step of introducing an impurity elementinto a semiconductor film is not necessary, a manufacturing process canbe simplified, and the number of masks can be reduced, leading to lowcost. Furthermore, in capacitor elements in plural stages which areprovided for a boosting circuit, by providing at least a capacitorelement in a first stage using a capacitor element in which twoelectrodes are formed using conductive films and providing capacitorelements in other stages using capacitor elements using semiconductorfilms, electric charge can be stored even in the case where voltageapplied to one end of the capacitor element in the first stage is lowerthan threshold voltage of the capacitor element using a semiconductorfilm. Thus, the area of the boosting circuit can be reduced and aboosting circuit can operate appropriately.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing an example of a semiconductor device of thepresent invention;

FIG. 2 is a view showing an example of a semiconductor device of thepresent invention;

FIG. 3 is a view showing an example of a semiconductor device of thepresent invention;

FIG. 4 is a view showing an example of a semiconductor device of thepresent invention;

FIG. 5 is a view showing an example of a semiconductor device of thepresent invention;

FIGS. 6A to 6C are views showing an example of a method formanufacturing a semiconductor device of the present invention;

FIGS. 7A to 7C are views showing an example of a method formanufacturing a semiconductor device of the present invention;

FIG. 8 is a diagram showing an example of a semiconductor device of thepresent invention;

FIG. 9 is a diagram showing an example of a semiconductor device of thepresent invention; and

FIGS. 10A to 10H are views each showing an example of a usage of asemiconductor device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the present invention will be explained below withreference to the accompanied drawings. However, the present inventioncan be implemented in various different modes, and it is to be easilyunderstood that various changes and modifications in modes and detailsthereof will be apparent to those skilled in the art without departingfrom the meaning and the scope of the present invention. Therefore, thepresent invention should not be interpreted as being limited to thedescription of the embodiment modes to be given below. It is to be notedthat, in embodiment of the present invention which will be explainedbelow, the same portions are denoted by the same reference numeralsthrough different drawings.

Embodiment Mode 1

This embodiment mode describes a structural example of a boostingcircuit of a semiconductor device of the present invention withreference to the drawings.

A semiconductor device described in this embodiment mode includes aboosting circuit formed by using a capacitor element in which aninsulating film is provided between two conductive films and a capacitorelement of a thin film transistor type. A capacitor element of a thinfilm transistor type refers to a capacitor element including a secondelectrode formed using a semiconductor film corresponding to asemiconductor film forming a channel formation region of a TFT; aninsulating film formed using an insulating film corresponding to a gateinsulating film of the TFT; and a first electrode formed using aconductive film corresponding to a gate electrode of the TFT. Thecapacitor element of a thin film transistor type is formed in the samestep as a TFT serving as a switch or the like provided for anotherintegrated circuit in a semiconductor device. Hereinafter, a specificstructure of a semiconductor device equipped with a boosting circuitdescribed in this embodiment mode is described.

A boosting circuit in a semiconductor device described in thisembodiment mode is formed by combining a capacitor element (bipolar) inwhich an insulating film is provided between two conductive films, and acapacitor element (unipolar) of a thin film transistor type in which atleast one of electrodes is formed using a semiconductor film. Here, theboosting circuit includes a first input terminal portion 101, a secondinput terminal portion 102, an output terminal portion 103, a firstcapacitor element 205 _(—1) to an n-th capacitor element 205 _(—n), afirst diode 104 _(—1) to an n-th diode 104 _(—n), and an inverter 106.The first diode 104 _(—1) to the n-th diode 104 _(—n), are connected inseries and are rectifying elements have a function of rectifying currentfrom the first input terminal portion 101 to the output terminal portion103. Here, the first input terminal portion 101 is connected to one ofelectrodes of the first diode 104 _(—1), and the other of the electrodesof the first diode 104 _(—1) is connected to one of electrodes of thesecond diode 104 _(—2) and an electrode of the first capacitor element205 _(—1) (see FIG. 1).

Further, in the structure shown in FIG. 1, the capacitor element of athin film transistor type has a structure in which one of electrodes (asecond electrode) is formed using a semiconductor film and the other ofthe electrodes (a first electrode) is formed using a conductive film.Specifically, the second electrode is formed using a semiconductor filmcorresponding to a semiconductor film forming a channel formation regionof a TFT which is provided for another integrated circuit; the firstelectrode is formed using a conductive film corresponding to a gateelectrode of the TFT; and the insulating film is formed using aninsulating film corresponding to a gate insulating film of the TFT.Accordingly, a step of introducing an impurity element into asemiconductor film to be the second electrode is not necessary, andthus, a manufacturing process can be simplified.

The second input terminal portion 102 is connected to a first wiring 107a and a second wiring 107 b. The first wiring 107 a is connected to oneof electrodes of each of the capacitor elements in odd-numbered stages,such as the first capacitor element 205 _(—1) and the third capacitorelement 205 _(—3). The second wiring 107 b is connected to one of theelectrodes of each of the capacitor elements in even-numbered stages,such as the second capacitor element 205 _(—2) and the fourth capacitorelement 205 _(—4).

Predetermined voltage (for example, power source voltage) is input tothe first input terminal portion 101, and boosted voltage is output fromthe output terminal portion 103. A clock signal is input to the secondinput terminal portion 102, and a signal (“High” or “Low”) and a signalobtained by inverting the signal by the inverter 106 are input to thefirst wiring 107 a and the second wiring 107 b, respectively.Accordingly, periodically, one of “High” and “Low” is applied to one ofthe electrodes of each of the capacitor elements in the odd-numberedstages (the first capacitor element 205 _(—1), the third capacitorelement 205 _(—3), and the like) connected to the first wiring 107 a,and the other of “High” and “Low” is applied to one of the electrodes ofeach of the capacitor elements in the even-numbered stages (the secondcapacitor element 205 _(—2), the fourth capacitor element 205 _(—4), andthe like) connected to the second wiring 107 b.

Here, in order to input a clock signal and a clock signal obtained byinverting the clock signal (phases thereof are different from each otherby 180°) to the first wiring 107 a and the second wiring 107 b,respectively, the inverter 106 is provided so as to be connected to thesecond input terminal portion 102 and one of the electrodes of thesecond capacitor element 205 _(—2). Alternatively, a structure may beemployed, in which clock signals having different phases are inputwithout providing the inverter 106.

In the boosting circuit described in this embodiment mode, at least acapacitor element in a first stage (here, the first capacitor element205 _(—1)) has a structure in which an insulating film is formed betweena first conductive film and a second conductive film, and othercapacitor elements (here, the second capacitor element 205 _(—2) to then-th capacitor element 205 _(—n)) each have a structure of a thin filmtransistor type. This is because in the case where the first capacitorelement 205 _(—1) is formed using a capacitor element of a thin filmtransistor type, there is a problem in that the capacitor element 205_(—1) does not serve as a capacitor when voltage applied to one end ofthe capacitor element of a thin film transistor type (voltage obtainedby subtracting threshold voltage of the rectifying element from inputvoltage) is lower than threshold voltage of the capacitor element of athin film transistor type. It is to be noted that in this specification,a capacitor element in a first stage refers to a capacitor element inwhich the lowest potential is stored among a plurality of capacitorelements provided for a boosting circuit. Here, the first capacitorelement 205 _(—1), which is connected to an output portion of the firstdiode 104 _(—1) which is a diode in the first stage and is connected tothe first input terminal portion 101 and an input portion of the seconddiode 104 _(—2), is the capacitor element in the first stage.Alternatively, a structure may be employed, in which the capacitorelement in the first stage is connected to not an output portion but aninput portion of the first diode 104 _(—1).

As described above, the boosting circuit is provided with not only acapacitor element having a structure in which an insulating film isprovided between a first conductive film and a second conductive filmbut also a capacitor element of a thin film transistor type.Accordingly, the insulating film forming the capacitor element can beformed to be thinned, and thus, the area of the capacitor element can bereduced. Further, by providing a capacitor element of a thin filmtransistor type, a step of introducing an impurity element into asemiconductor film overlapping with the other of electrodes in advancecan be omitted, and thus, a process can be simplified, which leads tolow cost. That is, with the structure shown in FIG. 1, reduction in areaof the capacitor element and appropriate operation of the boostingcircuit can be realized.

In this embodiment mode, at least the first capacitor element 205 _(—1)has a structure in which an insulating film, which is different from agate insulating film, is formed between conductive films In the casewhere the first capacitor element 205 _(—1) and other capacitor elements(here, the second capacitor element 205 _(—2) to the n-th capacitorelement 205 _(—n)) have the same capacitance, the first capacitorelement 205 _(—1) and the second capacitor element 205 _(—2) havedifferent element areas. In general, a gate insulating film is thinnerthan an insulating film which is different from a gate insulating film,and the first capacitor element 205 _(—1) becomes larger in area thanthe second capacitor element 205 _(—2).

Further, the first diode 104 _(—1) to the n-th diode 104 _(—n) may beelements each having a rectifying function, and each of the first diode104 _(—1) to the n-th diode 104 _(—n) can be formed using, for example,a PN diode, a PIN diode, a Schottky diode, a MIM (metal insulator metal)diode, a MIS (metal insulator semiconductor) diode, a diode-connectedtransistor, or the like.

Next, operation of the boosting circuit of the semiconductor device ofthis embodiment mode is briefly described with reference to FIG. 1.

The boosting circuit shown in FIG. 1 is a circuit including n pieces ofthe diodes 104 _(—1) to 104 _(—n), n pieces of the capacitor elements205 _(—1) to 205 _(—n), and the inverter 106, and can obtain outputvoltage of (VIN−VF)×n by inputting a clock signal, given that VIN isinput voltage and VF is forward voltage of the diode. The clock signalwhich is output from the second input terminal portion 102 is input toone end of each of the capacitor elements 205 _(—1) and 205 _(—3).Further, the clock signal which is output from the second input portion102 and then inverted by the inverter 106 is input to one end of thecapacitor element 205 _(—2). An anode for the diode 104 _(—2) is denotedby A, and a cathode for the diode 104 _(—2) is denoted by B. Electriccharge is supplied to each of the anode A and the cathode B with the useof the clock signal and the clock signal obtained by inverting the clocksignal, respectively. When a potential different between the anode A andthe cathode B exceeds the forward voltage VF of the diode, currentflows, whereby voltage on the cathode side is boosted. At this time, theboosted voltage is (VIN−VF). In the case where a plurality of circuitsis connected in series, output voltage is boosted by (VIN—VF) in everystage. In FIG. 1, n stages of circuits are connected in series; thus,output voltage is increased by (VIN−VF)×n. In this manner, the circuitshown in FIG. 1 serves as a boosting circuit.

Next, a specific structure of the boosting circuit of the semiconductordevice of the present invention is described with reference to FIGS. 2and 3. FIG. 2 is a schematic view of a top view of the boosting circuitof the semiconductor device, and FIG. 3 is a schematic view of across-sectional view taken along lines A1-A2 and B1-B2 in FIG. 2. FIGS.2 and 3 show the case where the diodes in FIG. 1 are formed usingdiode-connected thin film transistors.

The semiconductor device shown in FIGS. 2 and 3 includes semiconductorfilms 113 and 114 provided to have island-like shapes over a substrate110 with an insulating film 111 interposed between the semiconductorfilms 113 and 114, and the substrate 110; conductive films 117 and 118provided over the semiconductor films 113 and 114 with a gate insulatingfilm 115 interposed between the conductive films 117 and 118 and thesemiconductor films 113 and 114; a first conductive film 218 providedover the gate insulating film 115; an insulating film 119 provided tocover the gate insulating film 115 and the conductive films 117 and 118;and conductive films 120 a, 120 b, and 121 b, and a second conductivefilm 231 provided over the insulating film 119.

The semiconductor film 113 includes a channel formation region 113 aprovided below the conductive film 117, and impurity regions 113 b whichare provided to be separated from each other by the channel formationregion 113 a. The conductive films 120 a and 120 b are electricallyconnected to the impurity regions 113 b which are provided to beseparated from each other. One of the impurity regions 113 b which areprovided to be separated from each other may be referred to as a sourceregion or a drain region, and one of the conductive films 120 a and 120b may be referred to as source electrode or a drain electrode.

In a thin film transistor including the semiconductor film 113, the gateinsulating film 115, and the conductive film 117 serving as a gateelectrode, the conductive film 117 and the conductive film 120 a servingas a source electrode or a drain electrode are electrically connected toeach other, and the thin film transistor serves as a diode. Theconductive film 120 a corresponds to one of the electrodes of the firstdiode 104 _(—1) in FIG. 1, and the conductive film 120 b corresponds tothe other of the electrodes of the first diode 104 _(—1) in FIG. 1.

The semiconductor film 114 includes a region 114 a provided below theconductive film 118, and impurity regions 114 b which are provided to beseparated from each other by the region 114 a. The conductive film 121 bis electrically connected to the impurity regions 114 b which areprovided to be separated from each other. The impurity regions 114 bprovided to be separated from each other are provided at the same timeas the impurity regions 113 b serving as a source region and a drainregion of the semiconductor film 113.

In the semiconductor film 114, the region 114 a is formed in the samestep as the channel formation region 113 a of the semiconductor film113. Therefore, the region 114 a and the channel formation region 113include almost the same impurity element.

In the capacitor element of a thin film transistor type including thesemiconductor film 114, the gate insulating film 115, and the conductivefilm 118, the conductive film 121 b connected to the impurity regions114 b which are provided to be separated from each other is provided.The semiconductor film 114 corresponds to the second electrode of eachof the second capacitor element 205 _(—2) to the n-th capacitor element205 _(—n) in FIG. 1. The conductive film 118 corresponds to the firstelectrode of each of the second capacitor element 205 _(—2) to the n-thcapacitor element 205 _(—n) in FIG. 1. The impurity regions 114 b of thesemiconductor film 114 are electrically connected to the second wiring107 b through the conductive film 121 b.

The first capacitor element 205 _(—1) can be formed using the firstconductive film 218, the insulating film 119, and the second conductivefilm 231. The first conductive film 218 can be formed using the samematerial as the conductive film 117 and the conductive film 118, and thesecond conductive film 231 can be formed using the same material as theconductive films 120 a, 120 b, and 121 b.

As described above, by using a gate insulating film as an insulatingfilm of a capacitor element, the area of the capacitor element can bereduced, whereby the semiconductor device can be made smaller. In thecase where a capacitor element of a thin film transistor type is used,one of electrodes thereof is formed using a semiconductor filmcorresponding to a semiconductor film forming a channel formation regionof a TFT provided for an integrated circuit, whereby a manufacturingprocess can be simplified and the number of masks can be reduced, whichleads to low cost. In the case where a capacitor element in which twoelectrodes are formed using conductive films and a capacitor element ofa thin film transistor type in which one of electrodes is formed using asemiconductor film are combined, at least a capacitor element in a firststage is provided to have a structure in which two electrodes areprovided using conductive films, whereby reduction in area of thecapacitor element and appropriate operation of the boosting circuit canbe realized.

It is to be noted that, although FIGS. 2 and 3 show the case where theconductive film 121 b electrically connected to the impurity regions 114b does not overlap with the conductive film 118, the conductive film 121b may be provided to cover the conductive film 118 (see FIGS. 4 and 5).In this case, reduction in area of the capacitor element and improvementin characteristics due to increase in capacitance are possible. FIG. 4is a schematic view of a top view of a boosting circuit of asemiconductor device, and FIG. 5 is a schematic view of across-sectional view taken along lines A1-A2 and B1-B2 in FIG. 4.

The structure of the semiconductor device described in this embodimentmode can be implemented by being freely combined with the structures ofthe semiconductor devices in other embodiment modes in thisspecification.

Embodiment Mode 2

In this embodiment mode, a method of manufacturing a semiconductordevice in the above-described embodiment mode is described withreference to FIGS. 6A to 7C.

First, an insulating film 111 which serves as a base is formed over asubstrate 110. The substrate 110 may be a glass substrate, a quartzsubstrate, a metal or stainless steel substrate which has an insulatingfilm formed over one surface, a plastic substrate which has sufficientheat resistance to withstand processing temperatures of this process, orthe like. When such a substrate 110 is used, there are no largerestrictions on its area or shape; therefore, when, for example, arectangular substrate which has a side of one meter or more is used asthe substrate 110, productivity can be improved markedly. A merit suchas this is a large advantage compared with the case of using a circularsilicon substrate. In the case of providing a circuit necessary to beoperated at high speed, an SOI substrate (Silicon On Insulator)substrate may be used. Further, when a separation layer is used betweenthe substrate 110 and the insulating film 111, a layer having a thinfilm transistor can be transposed to a substrate over which a conductivefilm or the like is formed, and as a result, a connection between aconductive film which is connected to the thin film transistor, and theconductive film which is over the substrate to which the conductive filmis transposed, can be simplified.

A layer which includes an oxide of silicon or a nitride of silicon isformed as the insulating film 111 using a sputtering method, a plasmaCVD method, or the like.

An oxide of silicon is a material which includes silicon (Si) and oxygen(O), and corresponds to silicon oxide, silicon oxynitride, siliconnitride oxide, and the like. A nitride of silicon is a material whichincludes silicon and nitrogen (N), and corresponds to silicon nitride,silicon oxynitride, silicon nitride oxide, and the like. The insulatingfilm which serves as the base may be a single layer or a stack oflayers. For example, in the case where the insulating film which servesas the base has a two-layer structure, a silicon nitride oxide layer isformed as a first layer and a silicon oxynitride layer is formed as asecond layer. Alternatively, in the case where the insulating film whichserves as the base has a three-layer structure, a silicon oxide layermay be formed as a first insulating film, a silicon nitride oxide layermay be formed as a second insulating film, and a silicon oxynitridelayer may be formed as a third insulating film. Alternatively, a siliconoxynitride layer may be formed as a first insulating film, a siliconnitride oxide layer may be formed as a second insulating film, and asilicon oxynitride layer may be formed as a third insulating film. Theinsulating film which serves as the base functions as a blocking filmwhich prevents penetration of impurities from the substrate 110.

Next, an amorphous semiconductor film (for example, a layer includingamorphous silicon) is formed over the insulating film 111. The amorphoussemiconductor film is formed to a thickness of 25 to 200 nm (preferably30 to 150 nm) using a sputtering method, an LPCVD method, a plasma CVDmethod, or the like. Next, the amorphous semiconductor film iscrystallized using a laser crystallization method, a thermalcrystallization method which employs RTA or an annealing furnace, athermal crystallization method which employs a metal element whichpromotes crystallization, a method in which a laser crystallizationmethod is combined with a thermal crystallization method which employs ametal element which promotes crystallization, or the like to form acrystalline semiconductor film. Subsequently, the obtained crystallinesemiconductor film is patterned into a desired shape to form crystallinesemiconductor films 113 and 114 (see FIG. 6A).

Briefly describing an example of a manufacturing process for thecrystalline semiconductor films 113 and 114, first, a plasma CVD methodis used to form an amorphous semiconductor film with a thickness of 66nm. Next, a solution which includes nickel, which is a metal elementthat promotes crystallization, is retained on the amorphoussemiconductor film, and the amorphous semiconductor film is thensubjected to dehydrogenation treatment (at 500° C. for one hour) andthermal crystallization treatment (at 550° C. for four hours) to form acrystalline semiconductor film. Subsequently, laser light irradiation isperformed as necessary and patterning treatment which employs aphotolithography method is performed, whereby the crystallinesemiconductor films 113 and 114 are formed. In the case of using a lasercrystallization method to form the crystalline semiconductor films, acontinuous wave or pulsed gas laser or solid-state laser is used. As agas laser, an excimer laser, a YAG laser, a YVO₄ laser, a YLF laser, aYAlO₃ laser, a glass laser, a ruby laser, a Ti:sapphire laser, or thelike is used. As a solid state laser, a laser which employs a crystal,such as YAG, YVO₄, YLF, or YAlO₃, which is doped with Cr, Nd, Er, Ho,Ce, Co, Ti, or Tm is used.

Further, when a metal element which promotes crystallization is used tocrystallize the amorphous semiconductor film, while there are advantagesin that crystallization can be performed at a low temperature in a shortperiod of time and the direction of crystals is uniform, there are alsodrawbacks in that because metal element remains on the crystallinesemiconductor film, off-state current increases and TFT characteristicsare not stable. Therefore, preferably an amorphous semiconductor filmwhich functions as a gettering site is formed over the crystallinesemiconductor film. Since it is necessary to include an impurity elementsuch as phosphorus or argon in the amorphous semiconductor film whichserves as the gettering site, preferably the amorphous semiconductorlayer is formed using a sputtering method by which argon can be includedin the amorphous semiconductor layer at a high concentration. Then, heattreatment (an RTA method, thermal annealing which employs an annealingfurnace, or the like) is performed and the metal element is diffusedinto the amorphous semiconductor film. Subsequently, the amorphoussemiconductor film which includes the metal element is removed. Thus,the amount of metal element included in the crystalline semiconductorfilm can be reduced or metal element included in the crystallinesemiconductor film can be removed from the crystalline semiconductorfilm.

Next, a gate insulating film 115 which covers the crystallinesemiconductor films 113 and 114 is formed. The gate insulating film 115includes an oxide of silicon or a nitride of silicon and is formed by aplasma CVD method, a sputtering method, or the like as a single layer ora stack of layers. Specifically, a layer including silicon oxide, alayer including silicon oxynitride, or a layer including silicon nitrideoxide is formed as a single layer, or such layers are used to form astack of layers.

Next, a first conductive film and a second conductive film are stackedover the gate insulating film 115 (see FIG. 6B). The first conductivefilm is formed to a thickness of 20 to 100 nm by a plasma CVD method, asputtering method, or the like. The second conductive film is formed toa thickness of 100 to 400 nm by a plasma CVD method, a sputteringmethod, or the like. The first conductive film and the second conductivefilm are formed using any one of the elements tantalum (Ta), tungsten(W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu),chromium (Cr), niobium (Nb), and the like, or of an alloy material or acompound material which includes such an element as a main constituent.Alternatively, they may be formed of a semiconductor material typifiedby polycrystalline silicon doped with an impurity element such asphosphorus. Examples which can be given of combinations of the firstconductive film and the second conductive film include a tantalumnitride layer and a tungsten (W) layer, a tungsten nitride layer and atungsten layer, a molybdenum nitride layer and a molybdenum (Mo) layer,and the like. Tungsten and tantalum nitride have high heat resistance,so when they are used to form the first conductive film and the secondconductive film, subsequent to the formation of the two layers, heattreatment for thermal activation can be performed. Further, in the caseof employing a three-layer structure rather than a two-layer structure,a stacked structure which includes a molybdenum layer, an aluminumlayer, and another molybdenum layer may be used.

Next, a resist mask is formed by a photolithography method, and anetching treatment is performed on the first conductive film and thesecond conductive film to form conductive films 117 and 118 which serveas gate electrodes and a conductive film 218 serving as a firstelectrode of a capacitor element (see FIG. 6C).

Next, a resist mask is formed by a photolithography method, and desiredn-type or p-type impurity regions 113 b and 114 b, a channel formingregion 113 a, and a region 114 a are formed in the crystallinesemiconductor films 113 and 114 using an ion doping method or an ionimplantation method. For example, in the case of imparting n-typeconductivity, an element which belongs to Group 15 of the periodic tablemay be used as an impurity element which imparts n-type conductivity.For example, phosphorus (P) or arsenic (As) is used as an impurityelement and is added to form n-type impurity regions. Further, in thecase of imparting p-type conductivity, a resist mask is formed using aphotolithography method, and an impurity element which imparts p-typeconductivity, for example, boron (B), is added to a desired crystallinesemiconductor film to form a p-type impurity region.

Next, an insulating film 119 is formed so as to cover the gateinsulating film 115 and the conductive films 117 and 118. The insulatingfilm 119 is formed by a sputtering method, a CVD method, an SOG method,a droplet discharge method, or the like, using an inorganic materialsuch as an oxide of silicon or a nitride of silicon; an organic materialsuch as a polyimide, a polyamide, benzocyclobutene, an acrylic, anepoxy, or a siloxane; or the like. Siloxane has a skeleton structureformed of bonds between silicon (Si) and oxygen (O). An organic groupcontaining at least hydrogen (for example, an alkyl group or an aromatichydrocarbon) is used as a substituent. A fluoro group may also be usedas a substituent. Alternatively, a fluoro group and an organic groupcontaining at least hydrogen may be used as a substituent. Further, theinsulating film which covers the gate insulating film and the conductivefilms may be a single layer or a stack of layers. When a three-layerstructure is used, a layer including silicon oxide may be formed as afirst layer of the insulating film, a layer including a resin may beformed as a second layer of the insulating film, and a layer includingsilicon nitride may be formed as a third layer of the insulating film.

Note that before forming the insulating film 119, or after forming oneor more thin films of the insulating film 119, heat treatment forrestoring the crystallinity of the semiconductor films, activating animpurity element which has been added to the semiconductor films, orhydrogenating the semiconductor films may be performed. As the heattreatment, thermal annealing, a laser annealing method, an RTA method,or the like may be used.

Then, the insulating film 119 is etched by a photolithography method toform contact holes which expose the impurity regions 113 b and 114 b(see FIG. 7A). Subsequently, a conductive film 154 is formed so that thecontact holes are filled (see FIG. 7B).

The conductive film 154 is formed as a single layer or as stacked layersby a plasma CVD method, a sputtering method, or the like using any ofthe elements titanium (Ti), aluminum (Al), or neodymium (Nd), or analloy material or a compound material which contains one of theabove-mentioned elements as its main constituent. An alloy materialcontaining aluminum as its main constituent corresponds to, for example,a material which has aluminum as its main constituent and includesnickel, or an alloy material which has aluminum as its main constituentand includes nickel and one or both of carbon and silicon. Theconductive films 120 a to 121 b may employ, for example, a stacked layerstructure which includes a barrier layer, an aluminum-silicon (Al—Si)layer, and another barrier layer; or a stacked layer structure whichincludes a barrier layer, an aluminum-silicon (Al—Si) layer, a titaniumnitride layer, and another barrier layer. Note that a barrier layercorresponds to a thin film formed from titanium, a nitride of titanium,molybdenum, or a nitride of molybdenum. Aluminum and aluminum siliconhave low resistance and are inexpensive; therefore, they are idealmaterials for forming the conductive films 120 a to 121 b. Further,formation of a hillock of aluminum or aluminum silicon can be preventedwhen upper and lower barrier layers are provided. Further, when abarrier layer is formed from titanium, which is a highly reducibleelement, even when a thin natural oxide film forms over the crystallinesemiconductor film, the natural oxide film is reduced, and thereforegood contact with the crystalline semiconductor film can be obtained.

Next, the conductive film 154 is selectively etched to form conductivefilms 120 a, 120 b, 121 a, and 121 b, each of which serves as a sourceelectrode or a drain electrode, and a conductive film 231 serving as asecond electrode of the capacitor element (see FIG. 7C).

Through the above-described steps, a semiconductor device is obtained,which includes a thin film transistor having the semiconductor film 113,the insulating film 115 to be a gate insulating film, and the conductivefilm 117 to be a gate electrode; a capacitor element having theconductive film 218 to be a first electrode, the insulating film 119,and the conductive film 231 to be a second electrode; and a capacitorelement of a thin film transistor type, which has the semiconductor film114 to be a second electrode, the insulating film 115, and theconductive film 118 to be a first electrode.

As described in this embodiment mode, a thin film transistor, acapacitor element of a thin film transistor type, and a capacitorelement in which two electrodes are formed using conductive films, canbe manufactured in the same steps.

Embodiment Mode 3

This embodiment mode describes a structure of a semiconductor devicewhich can transmit and receive information wirelessly (also referred toas an RFID (radio frequency identification system) tag, an RF tag, an IDtag, an IC tag, a wireless tag, an electronic tag, or a wireless chip)and has a memory with a built-in boosting circuit in the above-describedembodiment mode, with reference to the drawings.

The semiconductor device described in this embodiment mode has featuressuch as capability of transmitting and receiving information with anexternal device (a reader/writer) without contact, operation withoutbattery, and superiority in durability and weatherability. A memory isoften mounted on such a semiconductor device to improve its fuction.

One feature of the semiconductor device described in this embodimentmode is that reading and writing data are possible without contact.Transmission formats of data are roughly classified into three types,which are: an electromagnetic coupling type which conducts communicationthrough mutual induction by positioning a pair of coils so as to faceeach other; an electromagnetic induction type which conductscommunication through an induction field; and a radio wave type whichconducts communication by utilizing radio waves. Any type may be used.Moreover, an antenna used for the data transmission can be provided intwo ways: one is that the antenna is provided over a substrate where aplurality of elements and a memory element are provided, and the otheris that a terminal portion is provided over a substrate where aplurality of elements and a memory element are provided and an antennaprovided over another substrate is connected to the terminal portion.

This embodiment mode describes a structural example of a semiconductordevice of a case of providing an antenna over a substrate provided witha plurality of elements and a memory element, with reference to FIG. 8.

A semiconductor device shown in FIG. 8 includes an antenna circuit 401,a clock generation circuit 404, a power supply circuit 405, a controlcircuit 412, and a memory circuit 413 over a substrate 400. The antennacircuit 401 includes an antenna 402 and a resonant capacitor 403, andthe power supply circuit 405 includes a smoothing circuit 406 and aboosting circuit 407. The smoothing circuit 406 includes a diode 408which rectifies an alternating signal, and a smoothing capacitor 409,and the boosting circuit 407 includes a group of diodes 410 for boostingvoltage, and a group of capacitor elements 411. In addition to thesecircuits, a data modulation/demodulation circuit, a sensor, and the likemay be included.

In order to perform operation of writing data to the memory circuit,second voltage, which is higher than voltage used at the time ofreading, is necessary to be applied. As a method for generating thesecond voltage, a method for boosting voltage (first voltage) obtainedby smoothing a signal received by an antenna with the use of a boostingcircuit, can be used. By particularly applying the structure of thesemiconductor device in the above-described embodiment mode, the circuitarea can be reduced, whereby the size of the semiconductor device can bereduced.

The structure of the semiconductor device described in this embodimentmode can be implemented by being freely combined with the structures ofthe semiconductor devices in other embodiment modes in thisspecification. In addition, as the memory circuit, a write-once memory,an EEPROM, a flash memory, or the like may be used.

Embodiment Mode 4

This embodiment mode describes a structure of a battery (an RF (radiofrequency) battery) capable of being charged wirelessly, which has abuilt-in boosting circuit, in the above-described embodiment mode withreference to FIG. 9. An RF battery (a non-contact battery using radiofrequency) has features such as capability of charging-up an objectwithout contact, superiority in portability, and the like.

As shown in FIG. 9, an RF battery includes a second antenna circuit 502,a resonant capacitor 503, a capacitor 504 of a rectifier circuit, asmoothing capacitor 507, a capacitor 510 for battery, diodes 505 and 506which rectify an alternating signal, a diode 509 for backflowprevention, a regulator circuit 508, and a boosting circuit 511. Inaddition to these circuits, a sensor and the like may be included.

Next, operation of the RF battery is described with reference to FIG. 9.

Electric power output from the power supply 500 is oscillated throughthe first antenna circuit 501 and received by the second antenna circuit502 of the RF battery. A resonant frequency of the received electricwave is tuned to a specific frequency using the resonant capacitor 503.Then, the received voltage is rectified using the capacitor 504, thefirst diode 505, and the second diode 506. After smoothing the waveformof the received voltage using the smoothing capacitor 507, the receivedvoltage is stored in the capacitor 510 through the regulator.

The RF battery is not charged unless power source voltage (for example,2 V) exceeds a certain threshold. Thus, there is a problem in thatelectric power thereof is not stored when voltage less than or equal tothreshold voltage is input. Therefore, in the RF battery, the boostingcircuit 511 is provided in a subsequent stage of the regulator orprovided for a place, which is different from the regulator, over thesame circuit, so that electric power can be stored even when voltageless than or equal to threshold voltage is input.

The structure of the semiconductor device described in this embodimentmode can be implemented by being freely combined with the structures ofthe semiconductor devices in other embodiment modes in thisspecification.

Embodiment Mode 5

This embodiment mode describes examples of the application of thesemiconductor device capable of transmitting and receiving informationwirelessly, in the above-described embodiment mode. The semiconductordevice of the invention can be used for various applications, and can beapplied to any product whose information such as history can bewirelessly obtained by the semiconductor device so that the informationcan be effectively utilized for production, management, and the like ofthe product. For example, the semiconductor device of the invention canbe applied to bills, coins, securities, documents, bearer bonds,packaging containers, books, storage media, personal belongings, meansof transportation, foods, clothes, healthcare items, daily commodities,medicines, electronic devices, and the like. Examples of suchapplication will be described with reference to FIGS. 10A to 10H.

The bills and coins are currency in the market and include notes thatare circulating as the real money in specific areas (cash vouchers),memorial coins, and the like. The securities include checks,certificates, promissory notes, and the like (FIG. 10A). The documentsinclude driver's licenses, resident's cards, and the like (FIG. 10B).The bearer bonds include stamps, rice coupons, various gift coupons, andthe like (FIG. 10C). The packaging containers include paper for wrappinga lunch box or the like, plastic bottles, and the like (FIG. 10D). Thebooks include documents and the like (FIG. 10E). The storage mediainclude DVD software, video tapes, and the like (FIG. 10F). The means oftransportation include wheeled cycles or vehicles such as bicycles,vessels, and the like (FIG. 10G). The personal belongings include shoes,glasses, and the like (FIG. 10H). The foods include food items,beverages, and the like. The clothes include clothing, footwear, and thelike. The healthcare items include medical devices, health appliances,and the like. The daily commodities include furniture, lightingapparatuses, and the like. The medicines include medicament,agricultural chemicals, and the like. The electronic devices includeliquid crystal display devices, EL display devices, television devices(television receivers or thin television receivers), mobile phones, andthe like.

When a semiconductor device 80 is provided for bills, coins, securities,documents, bearer bonds, and the like, forgery thereof can be prevented.In addition, when the semiconductor device 80 is provided for packagingcontainers, books, storage media, personal belongings, foods, dailycommodities, electronic devices, and the like, the efficiency of aninspection system, a rental shop system, and the like can be improved.Further, when the semiconductor device 80 is provided for means oftransportation, healthcare items, medicines, and the like, forgery andtheft thereof can be prevented and wrong use of the medicines can beprevented. The semiconductor device 80 may be provided by, for example,being attached to the surface of an object or embedded in an object. Forexample, the semiconductor device 80 may be embedded in paper of a bookor embedded in an organic resin of a package.

In this manner, when the semiconductor device is provided for packagingcontainers, storage media, personal belongings, foods, clothing, dailycommodities, electronic devices, and the like, the efficiency of aninspection system, a rental shop system, and the like can be improved.In addition, when the semiconductor device is provided for means oftransportation, forgery and theft thereof can be prevented. Further,when the semiconductor device is implanted in creatures such as animals,identification of the individual creature can be easily carried out. Forexample, when the semiconductor device is implanted in creatures such asdomestic animals, not only the year of birth, sex, breed, and the likebut also health conditions such as body temperature can be easilymanaged. In particular, by using the semiconductor device in theabove-described embodiment mode, reduction in size of the semiconductordevice can be realized, and accordingly, the semiconductor device can beprovided for these articles so as not to be noticeable.

The method for manufacturing the semiconductor device described in thisembodiment mode can be applied to the semiconductor device in otherembodiment modes described in this specification.

This application is based on Japanese Patent Application serial No.2006-354427 filed with Japan Patent Office on Dec. 28, 2006, the entirecontents of which are hereby incorporated by reference.

1. A semiconductor device comprising: an antenna circuit; and a boosting circuit for boosting a voltage supplied through the antenna circuit, the boosting circuit comprising: a plurality of rectifying elements connected in series between an input terminal portion and an output terminal portion of the boosting circuit, each of the rectifying elements including an input portion and an output portion, with an input portion of a first one of the rectifying elements being connected to the input terminal portion; and a plurality of capacitor elements each including a first electrode, a second electrode, and an insulating film interposed between the first electrode and the second electrode, wherein the first electrode of a first one of the plurality of capacitor elements is connected to an output portion of the first one of the plurality of rectifying elements; wherein the first electrode of a k-th one of the plurality of capacitor elements is connected to an output portion of a k-th one of the rectifying elements and to an input portion of a (k+1)th one of the rectifying elements (where k is an integer of 2≦k≦(n-1)); wherein the first electrode of the first one of the plurality of capacitor elements comprises a first conductive film and the second electrode of the first one of the plurality of capacitor elements comprises a second conductive film; and wherein the first electrode of at least another one of the plurality of capacitor elements comprises the first conductive film and the second electrode of at least another one of the plurality of capacitor elements comprises a semiconductor film.
 2. The semiconductor device according to claim 1, wherein the first electrode of the second one of the plurality of capacitor elements comprises the first conductive film and the second electrode of the second capacitor element comprises a semiconductor film.
 3. The semiconductor device according to claim 1 further comprising a first wiring and a second wiring wherein the second electrode of one of the plurality of capacitor elements is connected to one of the first wiring and the second wiring and the second electrode of an adjacent one of the plurality of capacitor elements is connected to the other one of the first wiring and the second wiring.
 4. The semiconductor device according to claim 3, wherein the first wiring is configured to supply a first signal and the second wiring is configured to supply a second signal which is an inverse of the first signal.
 5. The semiconductor device according to claim 1, wherein the insulating film of the another one of the plurality of capacitor elements is thinner than the insulating film of the first one of the plurality of capacitor elements.
 6. The semiconductor device according to claim 1, wherein each of the plurality of the rectifying elements comprises a diode-connected thin film transistor having a gate electrode that comprises the first conductive film.
 7. The semiconductor device according to claim 1, wherein the boosting circuit is formed by using an SOI substrate.
 8. The semiconductor device according to claim 1, wherein the boosting circuit is electrically connected to the antenna circuit through a smoothing circuit.
 9. A semiconductor device comprising: an antenna circuit; and a boosting circuit for boosting a voltage supplied through the antenna circuit, the boosting circuit comprising: at least first, second and third rectifying elements connected in series between an input terminal portion and an output terminal portion of the boosting circuit, each of the rectifying elements including an input portion and an output portion, with an input portion of the first one of the rectifying elements being connected to the input terminal portion; and at least first and second capacitor elements each including a first electrode, a second electrode, and an insulating film interposed between the first electrode and the second electrode, wherein the first electrode of the first one of the plurality of capacitor elements is connected to an output portion of the first one of the plurality of rectifying elements; wherein the first electrode of the second one of the plurality of capacitor elements is connected to an output portion of the second one of the rectifying elements and to an input portion of the third one of the rectifying elements; wherein the first electrode of the first one of the plurality of capacitor elements comprises a first conductive film and the second electrode of the first one of the plurality of capacitor elements comprises a second conductive film; and wherein the first electrode of the second one of the plurality of capacitor elements comprises the first conductive film and the second electrode of the second one of the plurality of capacitor elements comprises a semiconductor film.
 10. The semiconductor device according to claim 9 further comprising a first wiring and a second wiring wherein the second electrode of one of the plurality of capacitor elements is connected to one of the first wiring and the second wiring and the second electrode of an adjacent one of the plurality of capacitor elements is connected to the other one of the first wiring and the second wiring.
 11. The semiconductor device according to claim 10, wherein the first wiring is configured to supply a first signal and the second wiring is configured to supply a second signal which is an inverse of the first signal.
 12. The semiconductor device according to claim 9, wherein the insulating film of the another one of the plurality of capacitor elements is thinner than the insulating film of the first one of the plurality of capacitor elements.
 13. The semiconductor device according to claim 9, wherein each of the plurality of the rectifying elements comprises a diode-connected thin film transistor having a gate electrode that comprises the first conductive film.
 14. The semiconductor device according to claim 9, wherein the boosting circuit is formed by using an SOI substrate.
 15. The semiconductor device according to claim 9, wherein the boosting circuit is electrically connected to the antenna circuit through a smoothing circuit. 